But fewer than half showed significant links to disease risks in larger follow up studies.

And just one in five increased a patient's relative risk by more than 1.37, when one means no risk and two is double the risk. The median relative risk reported by the studies was 2.5.

"We found that a large majority of these highly cited papers suggested substantially stronger effects than that found in the largest study of the same markers and outcomes," says Ioannidis, a prominent analyst of scientific methods.

"Many of these studies were relatively small and among the first to report on the association of interest," he say.

"Discoveries made in small studies are prone to overestimate or underestimate the actual association. Interest in publishing major discoveries leads to selective reporting from chasing significance."

Even scientists are prone to manipulating their figures to show more dramatic results, and often times meta-analyses -- or a look at results from multiple independent studies -- will over time reveal the true nature of the link, he added.

"We have to learn to trust the bigger picture," says Ioannidis. "And it's better to demand this proof upfront rather than waiting for it to happen on a case-by-case basis."